This invention relates to a thermal transfer recording sheet. More particularly, it relates to a thermal transfer recording sheet containing inorganic fine particles having a plate-like or lamellar structure in a support so as to lessen wear of a thermal head.
Recently, there have been developed thermal transfer recording materials which form transferred images on plain paper, using thermal printers, thermal facsimiles, and the like. This thermal tranffer recording method is noticed because the maintenance of apparatus is easy due to its simple structure, the price and maintenance cost of apparatus are low, clear and durable recording is possible with low energy, and colored recording is possible with relative ease by using multi-color ink sheets.
According to the thermal transfer recording method, the recording is accomplished by placing an image receiving sheet on a hot-melt or heat sublimable coloring ink layer coated on a support of a thermal transfer recording sheet, heating selectively the hot-melt or heat sublimable ink layer by a thermal head depending on electric signals from the non-coated side of the thermal transfer recording sheet so as to transfer an image on the image receiving sheet, and separating the image receiving sheet from the thermal transfer recording sheet. At present, single color (black) recording is practically used in word processors, facsimiles, printers, and the like. Further, multi-color recording is to be used practically in color copies and printers for CAD (Computer Aided Design).
As the support of these thermal transfer recording sheets used for such recording, there are used condenser paper with 10 to 13 .mu.m thick and synthetic resin films with 3 to 15 .mu.m thick. Among them, a polyester film is preferably used considering strength, heat resistance and a cost. The surface of the thermal transfer recording sheet to be contacted with a thermal head can be coated with a heat resistance improving agent with a thickness of 0.1 to several microns in order to withstand the heat of the thermal head. In the case of using a synthetic resin film such as a polyester film as the support, inorganic particles of silicon oxide, calcium carbonate or aluminum oxide are added to the synthetic resin film as a slipping agent in order to improve take-up characteristics of the synthetic resin film after film forming. But in such a case, these inorganic particles form projections of about 0.5 .mu.m or less on the film surface. Even if a heat resistant layer is coated over the film surface having such projections, the projections of about 0.5 .mu.m or less are still retained on the film surface, since the thickness of the heat resistant layer is so small and insufficient to fill vacant spaces among projections.
On the other hand, materials having good thermal conductivity are often included in the synthetic resin film support in order to better the thermal conductivity and to improve the transfer sensitivity of coloring inks when contacted with the thermal head (Japanese Patent Unexamined Publication Nos. 58-55293, 59-162090 and 59-174392). In such a case, projections are also formed on the surface of the synthetic resin film to be contacted with the thermal head.
Such projections damage the surface of the thermal head at the time of thermal transfer recording due to the contact with the thermal head surface under pressure and produce physical wear, and in the worst case, destroy the thermal head. Removal of such a disadvantage has been desired.